Again, I try to bring everyone back to the original post. No skill points to build ammo, every time you upgrade weapon skill you get that ammo build Lv by default. That way you don't have to rework the skills and the points.
As to vendor ammo, many weapons you cant buy vendor ammo for. And a part of the game is making your ship better, from Lv1 on up every time you change a shield, reactor, engine, ect you are improving your ship. it would be unreasonable to ask someone to not want to get the best equipment his ship can use.
Again, by ONLY reason for the build ammo skill for these 2 ships are to make the play experience more enjoyable for each. I honestly think this one simple change would see more of each of these classes.
I don't propose building anything more than ammo period as a change. Again the only reason for the change would be a more enjoyable gaming experience while playing these two classes, which is why we all play, to have fun.
Now, you did make one point, make all Explorers Lv9 Beam users, which makes way less sense than giving them the simple ability to make ammo that it uses.